Search results for "Hydrogen"

Ability of Kocuria varians LTH 1540 To Degrade Putrescine: Identification and Characterization of a Novel Amine Oxidase.

2015

This work describes the identification and characterization of an amine oxidase from Kocuria varians LTH 1540 (syn. Micrococcus varians) primarily acting on putrescine. Data from MALDI-TOF MS/MS and the identification of Δ(1)-pyrroline as degradation product from putrescine indicate that the enzyme is a flavin-dependent putrescine oxidase (PuO). Properties of partially purified enzyme have been determined. The enzyme oxidizes diamines, putrescine and cadaverine, and, to a lesser extent, polyamines, such as spermidine, but not monoamines. The kinetic constants (Km and Vmax) for the two major substrates were 94 ± 10 μM and 2.3 ± 0.1 μmol/min·mg for putrescine and 75 ± 5 μM and 0.15 ± 0.02 μmo…

A DFT study of the mechanism of NHC catalysed annulation reactions involving α,β-unsaturated acyl azoliums and β-naphthol.

2016

The mechanism of NHC catalysed annulation reactions involving an α,β-unsaturated acyl azolium and β-naphthol has been studied using DFT methods at the MPWB1K/6-311G(d,p) level in toluene. For the C-C bond formation step, which corresponds to the rate- and stereo-determining step of this NHC catalysed reaction, the two competitive addition modes, i.e. the 1,2- and the 1,4-additions, have been studied. In toluene, acyl azolium forms an ion pair (IP) with the counterion chloride anion. Interestingly, β-naphthol forms a hydrogen bond with the chloride anion of IP, increasing the nucleophilic character of β-naphthol and the electrophilic character of the acyl azolium moiety. For the first time, …

1989

Poly(9,10-dihydroanthrylenetrimethylene) (2) comprises a novel chain-type structure in which 9,10-dihydroanthracene units are linked by flexible spacer groups. Upon dehydrogenation with sulfur at elevated temperature, polymer 2 is converted into the corresponding polyanthrylene system 3. NMR- and UV-spectroscopic data provide firm evidence for the dehydrogenation process. The polymer 3 was subjected to reduction with active lithium, and the resulting polyanions were characterized by NMR spectroscopy and by quenching experiments. It appears that each anthracene unit of the chain can be charged with two electrons.

Low-Molecular-Weight Organic Acid Complexation Affects Antimony(III) Adsorption by Granular Ferric Hydroxide.

2019

Antimony(III) mobility in natural aquatic environments is generally enhanced by dissolved organic matter. Tartaric acid is often used to form complexes with and stabilize dissolved Sb(III) in adsorption studies. However, competition between such low-molecular-weight organic acid complexation and adsorption of Sb(III) has received little attention, which prompted us to measure Sb(III) adsorption by iron oxyhydroxide adsorbents commonly used in water treatment plants. Sb K-edge X-ray absorption fine structure (EXAFS) spectra gave Sb–O and Sb–Fe distances and coordinations compatible with a bidentate binuclear inner-sphere complex with trigonal Sb(O,OH)3 polyhedra sharing corners with Fe(O,OH)…

Iron(II) Complexes with Scorpiand-Like Macrocyclic Polyamines: Kinetico-Mechanistic Aspects of Complex Formation and Oxidative Dehydrogenation of Coo…

2017

The Fe(II) coordination chemistry of a pyridinophane tren-derived scorpiand type ligand containing a pyridine ring in the pendant arm is explored by potentiometry, X-ray, NMR, and kinetics methods. Equilibrium studies in water show the formation of a stable [FeL]2+ complex that converts to monoprotonated and monohydroxylated species when the pH is changed. A [Fe(H–2L)]2+ complex containing an hexacoordinated dehydrogenated ligand has been isolated, and its crystal structure shows the formation of an imine bond involving the aliphatic nitrogen of the pendant arm. This complex is low spin Fe(II) both in the solid state and in solution, as revealed by the Fe–N bond lengths and by the NMR spect…

Cooperative Effects in Aminothiols: Acid-Base Equilibria and the Molecular Structure of 2-(N, N-Dimethylaminomethyl)thiophenol

2008

Abstract 2-(N,N-Dimethylaminomethyl)thiophenol, (1, HL), is present as a non-zwitterionic aminothiol in the solid state, exhibiting an intramolecular S-H···N hydrogen bond. The S···N distances of the two independent molecules in the asymmetric unit are 2.929(10) and 3.050(10) Å. This structural feature is also present in an ab initio (MP2/6-31G*) optimized molecular structure. The investigation of the hydrogen bond by ab initio methods supports an n(N)-σ *(S-H) interaction as the reason for this bond type. On the basis of data from potentiometric acid-base titrations of a 0.01 M aqueous solution of [H2L]Cl with a 0.1 M aqueous solution of sodium hydroxide, values of 4.09±0.01 and 11.50±0.01…

Role of pH in the synthesis and growth of gold nanoparticles using L-asparagine: a combined experimental and simulation study

2020

Abstract The use of biomolecules as capping and reducing agents in the synthesis of metallic nanoparticles constitutes a promising framework to achieve desired functional properties with minimal toxicity. The system’s complexity and the large number of variables involved represent a challenge for theoretical and experimental investigations aiming at devising precise synthesis protocols. In this work, we use L-asparagine (Asn), an amino acid building block of large biomolecular systems, to synthesise gold nanoparticles (AuNPs) in aqueous solution at controlled pH. The use of Asn offers a primary system that allows us to understand the role of biomolecules in synthesising metallic nanoparticl…

Conformational analysis of α,β-poly(N-hydroxyethyl)-dl-aspartamide (PHEA) and α,β-polyasparthydrazide (PAHy) polymers in aqueous solution

1998

Abstract α,β-Poly(N-hydroxyethyl)- dl -aspartamide (PHEA) and α,β-polyasparthydrazide (PAHy) are synthetic polymers previously studied for biomedical applications. We report here the results of a small-angle X-ray scattering analysis carried out on these two macromolecules in aqueous solution. The data obtained indicate that the two polymers assume remarkably different conformations in aqueous solution, although the backbone is supposed to be the same for the two chains. PHEA can be represented by a random coil conformation, whereas PAHy can be described in terms of an elliptical cylinder characterized by an almost planar structural arrangement with the backbone refolded on itself in a fash…

Thermodynamic and kinetic studies on the Cu2+ coordination chemistry of a novel binucleating pyridinophane ligandElectronic supplementary information…

2003

The synthesis and coordination chemistry of the novel pyridine-functionalized ligand 2,6,9,12,16-pentaaza[17]-(2,6)pyridinophane (L1) is described. The compound behaves as a hexaprotic base in aqueous solution. NMR studies indicate a protonation pattern in which the sp2 pyridine nitrogen (N(py)) does not undergo a net protonation although it is involved in formation of hydrogen bonds. L1 forms mono and binuclear hydroxylated complexes. The crystal structure of [CuL1](ClO4)2 shows a square planar coordination for Cu2+ with the pyridine and the three central nitrogens of the chain forming the vertices of the square. The benzylic nitrogens could be occupying the axial positions of a strongly a…

p-Nitrophenolate: A Probe for Determining Acid Strength in Ionic Liquids

2009

In order to obtain an acidity scale in room-temperature ionic liquid solutions, the protonation equilibrium of sodium p-nitrophenolate in [bm(2)im][NTf(2)] and in [bmpyrr][NTf(2)], at 298 K, has been studied by means of spectrophotometric titration. Carboxylic acids differing in both structure and in water solution strength have been used. Data collected indicate that in the analyzed ionic liquid solutions carboxylic acids are less dissociated than in water solution. Furthermore, by virtue of a mutual interaction, the studied equilibrium seems to be affected by both the nature of the ionic liquids and the carboxylic acids.